Internal-combustion engines – Poppet valve operating mechanism – Electrical system
Reexamination Certificate
2000-04-26
2001-08-07
Lo, Wellun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Electrical system
C251S129010, C251S129160
Reexamination Certificate
active
06269784
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
BACKGROUND OF THE INVENTION
The present invention relates to actuators for the intake and exhaust valves of internal combustion engines, and specifically to an electronically actuable engine valve providing a signal indicating the valve position.
Electrically actuable valves allow improved engine control. Unlike valves actuated mechanically by cam shafts and the like, the timing on electrically actuable valves can be more freely varied during different phases of engine operation by a computer-based engine controller.
One type of actuator for such a valve provides a disk-shaped armature which moves back and forth between two cylindrical electromagnets. The armature is attached to the valve stem of the valve and is moved against the force of two opposing springs each positioned between the armature and an opposing core. In an unpowered condition, the armature is held in equipoise between the two cores by the opposing spring forces.
During operation, the armature is retained against one of the cores by a “holding” current in the retaining electromagnet. The spring between the armature and the retaining core is compressed while the other spring is stretched.
A change of state is effected, opening or closing the valve, by interrupting the current holding the armature in place. When this occurs, the energy stored in the compressed and stretched springs accelerates the armature off of the releasing core toward the opposing receiving core. When the armature reaches the receiving core, that core is energized with a “holding” current to retain the armature in position against its surface.
In a frictionless system, the armature reaches a maximum velocity at the midpoint between the two cores (assuming equal spring forces) and just reaches the receiving core assembly with zero velocity. In a physically realizable system in which friction causes some of the stored energy of the springs to be lost as heat, the armature will not reach the receiving core unless the energy lost to friction is replaced. This is accomplished by creating a “capture” current in the receiving coil which produces a magnetic force to attract the armature and pull it to the core. The capture current is necessarily initiated before the armature contacts the receiving core. Once the armature is captured by the receiving coil, the current can be reduced to a holding level sufficient to hold the armature against the core until the next transition is initiated.
Capture of the approaching armature requires that the capture current be of sufficient magnitude to draw the armature to the core. However, it is equally important that the speed at which the armature strikes the core be limited to prevent armature damage and/or core damage and to minimize impact noise. During valve closing, control of the capture current is necessary to limit valve-seating velocity and thereby to prevent valve and/or valve seat damage or premature valve wear and to minimize valve-seating noise. If the capturing current is turned on too soon (or is too great in magnitude), the armature may be accelerated into the core and the valve into its seat at excessive velocity. Conversely, the armature may not be captured by the receiving core and the valve may not close if the capture current is turned on too late (or is too low in magnitude). Therefore, it is important to know armature position and velocity as it approaches the receiving core to ensure that the capture current is initiated at the proper time or amount to ensure proper capturing of the approaching armature.
Electronic position sensors may be attached to the valve stem for this purpose. Unfortunately position sensors that are sufficiently accurate and robust enough to survive in the environment of an internal combustion engine are expensive and thus impractical.
BRIEF SUMMARY OF THE INVENTION
The present inventor has recognized that a signal providing an indication of the position of the armature with respect to the cores may be derived from a back electromagnetic force (“back EMF”) generated in the receiving coil typically when the receiving coil is energized with a small sensing current. The back EMF is dependent in magnitude on the proximity of the armature to the receiving coil and thus provides an indication of armature position that may be used for more accurate valve actuation or other purposes.
Specifically then, the present invention provides a controller for an electrically actuable engine valve, the valve having an actuation coil producing a magnetic field to attract a movable armature communicating with a valve. The controller includes a current control circuit receiving a valve actuation signal (such as from an engine controller) and a drive current signal to provide current to the actuation coil when the valve actuation signal is present and as a function of the value of the drive current signal. An armature detector senses a back EMF resulting from an approach of the movable armature toward the actuation coil and based on this detection, a soft seat circuit adjusts the drive current signal to the current control circuit as a function of the back EMF sensed by the armature detector.
Thus, it is one object of the invention to provide an electrically actuable valve that produces a position output signal such as may be used to precisely control the actuation current to the valve to reduce wear on the valve assembly. Unlike systems which detect only the time at which the armature strikes the coil, the present invention allows monitoring of the approach of the armature as is necessary for soft seating of the valve against the valve seat.
The current control circuit may provide a hysteretic control, outputting current to the actuation coil if the current through the actuation coil drops below a predetermined low threshold and disconnecting current from the actuation coil if the current rises above a predetermined high threshold.
It is thus another object of the invention to provide an efficient controller allowing monitoring back EMF. Hysteretic control operates in a switched mode to reduce power dissipation and facilitates measurement of the faint back EMF signal during periods when the hysteretic control is not outputting current.
The armature detector may monitor the frequency of the switching of the current control circuit in hysteretic mode.
Thus it is another object of the invention to provide an extremely simple measurement output of armature position. Back EMF affects the decay of current in the actuation coil during periods when the hysteretic control is off thus affecting the frequency of switching of the hysteretic control. This frequency may be readily measured.
Alternatively, the armature detector may directly monitor the rate of change of current in the actuation coil after the current control circuit disconnects current from the actuation coil to measure back EMF.
Thus it is another object of the invention to provide a measurement of back EMF that is independent from the changes in control current that may be desired during different stages of the actuator closure.
The soft seat circuit may be sensitive to a seating level of back EMF from the armature detector occurring upon contact of the armature and the actuation coil. The soft seating circuit may provide a capture drive current signal (producing a capture current in the actuation coil) before the seating level is detected and a holding drive current signal (providing a holding current in the actuation coil) after the seating level is detected wherein the holding current is less than the capture current.
Thus it is another object of the invention to provide ample capture current while significantly decreasing the power consumption of the valve during holding.
The soft seat circuit may also be sensitive to a capture level of back EMF from the armature detector occurring prior to contact of the armature in the actuation coil. The soft seating circuit may provide a sensing drive current signal (providing a sensing cu
Lo Wellun
Quarles & Brady LLP
Visteon Global Technologies Inc.
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